The present invention relates to an improved cover for a turbofan engine blade of a gas turbine engine.
Some turbofan aircraft engines have a fan blade design that requires outward radial movement of the fan blade. That is, a fan blade pin pinning the blade in place has to be removed to allow removal of the fan blade. The blade then has to be moved out from the engine centerline before it can be removed from the engine. A recess or pocket is required in the structural containment fan case to allow such blade removal. This recessed pocket or blade port must have a removable cover to maintain a smooth flowpath surface on the inside diameter of the containment case. In the existing art, this blade port cover is typically made of cast aluminum, with threaded inserts to facilitate installation.
Unfortunately, the blade port and cover can have a deleterious effect during a fan blade failure. The blade port area forms a hard and massive feature. This feature behaves differently from the remainder of the containment case. If a fragment of a broken fan blade impacts this area, it decelerates more quickly and has a greater chance of impacting other fan blades, increasing the probability that they will fail as well. Further, the cover can readily be torn off by such an impact, becoming an unrestrained mass that can cause additional damages to other blades upon impact.
It would be desirable, then, to provide an improved structure for the blade port area of a turbofan aircraft engine.
To improve the existing cover structure, a frangible material is proposed for forming the body of the blade port cover. Additionally, a geometric design can be applied to the cover, incorporating multiple small-radius inside corners to act as initiation points for brittle fracture.
Accordingly, the present invention provides an improved structure for forming the blade port area of a turbofan aircraft engine.